Early embryonic erythropoiesis and myogenesis will be analyzed in cell culture at the chromatin level. An explanation for the role of 5-bromodeoxyuridine in reversibly inhibiting the expression of differentiation will be sought through its effect on the specificity of transcription of chromatin. We plan to focus on the role of particular chromatin components in deciding stage-specific chromatin transcription to particular RNAs. Erythroblast cell surface changes both during transformation with tumor viruses and during normal differentiation will be studied. We plan to continue work on the cell surface changes during myoblast differentiation to myotubes in both normal and dystrophic situations and in relation to the differentiation of acetylcholine receptors. Bibliographic references: Teng, N.N.H. and Ingram, V.M. Cell Surface Alteration During Myogenesis In Vitro. Presented at the 14th Annual Meeting of the American Society for Cell Biology, San Diego (1974).